TWI has developed techniques for producing realistic imperfections/defects and, in the case of cracks, the desired morphology, including roughness, angles of tilt and skew to the surface.
The most important criterion in producing defects or imperfections is that they must accurately simulate flaws which can occur in welded components and structures. TWI can reliably produce weld specimens with imperfections/defects such as:
- Lack of root fusion
- Lack of penetration
- Lack of sidewall or interrun fusion
- Joint misalignment
- Solidification cracking
- Cluster cracking
- Heat affected zone (hydrogen) cracking
- Brittle fracture or fatigue cracks
- Under or overfill of weld metal
- Inclusions (slag or metallic)
Some of these are produced by simulating poor welding practice (lack of root fusion and porosity), or by welding with techniques such as TIG bridging to obtain lack of side wall fusion or by welding under crack promoting conditions.
TWI has developed techniques for depositing all of these and offers a service that will incorporate a qualification procedure that can be verified by on-site non destructive testing by surface crack detection, ultrasonic or radiographic inspection and/or sectioning to demonstrate and qualify procedures that will be incorporated into the welded test piece
When producing a test block for NDT validation, training or development, it is important that the implanted defects are as realistic as possible. However, test blocks containing machined defects (such as side-drilled holes), are not representative of real defects.
This service can be offered to Member companies of TWI as project work undertaken by qualified welding engineers and uniquely with the support of in-house experts in non-destructive testing, materials and structural integrity.
By developing and validating NDT procedures on defect specimens, one can obtain quicker and more accurate inspection in production.
The Arc Welding Department at TWI has a longstanding, 20-year-expertise with the intentional creation of specific types of weld defects or imperfections. These have been used by major NDT centres and TWI's clients in validation of NDT techniques, such as ultrasonic and radiographic inspection, as well as training of inspection personnel in the detection of flaws.
Defective specimens for NDT validation have been produced for a variety of projects in the Oil & Gas, Power Generation (Nuclear) and Petrochemical industry sectors. A summary of TWI's capabilities, as well as a case study, can be found here.
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